1. Field of the Invention
This invention relates to a thermal transfer recording apparatus, which is improved in terms of the method for transfer of a top coat layer from an ink film.
2. Description of the Related Art
The thermal transfer recording apparatus is provided with a platen roller and a thermal head as a heating element, which is freely pressed against and separated from the platen roller, and conveys a recording paper through the contacting surface between the platen roller and the thermal head. An ink film which has, for example, an ink with sublimating properties applied to one surface is conveyed into the contacting surface between the recording paper and the thermal head. This ink film is unwound from a supply reel and wound on a take-up reel.
An ink film, which has ink layers in colors such as yellow, magenta and cyan, and a top coat layer sequentially applied in the order on the surface of a film base, is used when single thermal head is operated for reproducing a color image on a recording paper. And the ink film produces a color print by the overlapping of monochromatic images.
The top coat layer is a layer formed by thermally transferring a top coating agent as a laminating resin onto the recording paper at the final stage of printing for the purpose of covering a printed area on the recording paper and preventing the printed area from fading. The recording apparatus of this kind is designed to transfer the top coat layer of a size slightly larger than the printed area, or the image area on the recording paper.
Incidentally, the ink layers in yellow, magenta, cyan, etc. are formed of subliming dyes. The ink layers are transferred by virtue of sublimation (diffusion). Accordingly, there is practically no possibility that defective transfer occurs. In contrast, the top coat layer is formed of a transparent resin. The top coat transfer requires being infallibly adhered to the recording paper at a suitable temperature. It is, however, difficult to fulfil the requirement. Thus, the top coat layer at times fails to be perfectly transferred to the recording paper because the desired temperature of the thermal head for transferring the top coat layer cannot be kept constant to the initial area on which the top coat layer is applied.
In the conventional recording paper, the background area other than the image area is nearly always in a white color. So long as the top coat layer is transferred in a size slightly larger than the image area, therefore, any portion of only nominal defective transfer is not prominent and is incapable of seriously affecting the quality of the finished print because It is located in the white background area.
Recently, a shop such as a processing laboratory, which prints out photographs, deals with a so-called index print, which reproduces the information recorded in a plurality of frames of a negative film on single recording paper. This index print is occasionally required to impart colors to the background area other than the image area. In this case, the defective top coat transfer appears conspicuous to the extent of posing a problem.
The thickness of the recording paper on the lateral edge of the recording paper laid on the platen roller results in the formation of a gap in an area enclosed by the outer periphery of the platen roller, the edge of the recording paper and the top coat layer. The gap has such problems as inhibiting perfect transmission of the heat from the thermal head and inducing defective top coat transfer in the edge area of the top coat layer opposite the vicinities of the lateral edge of the recording paper.
A recording paper, which has such a half-cut thickness line like a sheet of separable and self-adhesive labels or printed matter, is occasionally used. The recording paper similarly produces a gap on the half-cut line. The gap inhibits perfect transfer of heat and induces defective top coat transfer to the recording paper behind the half-cut line, namely in the image area on the downstream side in the direction of printing.